Abstract

Abstract

Spatial distribution of crop residues incorporated by tillage is generally unknown even though the soil environment for roots, soil microbes, and water flux may be greatly affected. Variations in depth and concentration of oat (Avena sativa L.) residue and tracers (ceramic spheres and polyethylene chips) were measured after incorporation by disk, chisel, or moldboard plow as a primary tillage. Depth distribution of root tissue in an untilled area was also measured. In 1987 and 1988, 60 to 120 soil cores (1.8-cm diam.) per treatment were taken to a 30-cm depth immediately after tillage and sectioned into 2-cm increments (a 5-cm3 volume). Residue amount, tracer presence, and soil bulk density were measured in each 5-cm3 sample. Moldboard-plowing treatments incorporated crop residue to a depth of 28 cm; chiseling and disking incorporated residue to 10 cm. Despite differences in depth of incorporation between tillage treatments, residue and tracers were generally in a 10-cm band of each 30-cm-deep core from all tillage systems. Frequency distributions of residue concentration in individual 5-cm3 samples were not normal (Gaussian); rather, they were monotonic and positively skewed. Maximum concentrations of crop residue in a 5-cm3 sample (135.0 mg cm−3 in 1987 and 48.1 mg cm−3 in 1988) were similar among tillage treatments and were greater than the average concentration by a factor of 10 for disk and chisel and 30 for moldboard plow. Samples containing incorporated residue had a distinctly higher soil porosity than samples in general. Primary tillage buries crop residue without effectively dispersing in a microscopic scale throughout the tilled zone. Ceramic spheres and polyethylene chips worked equally well as tracers for incorporated residue.

Please view the pdf by using the Full Text (PDF) link under 'View' to the left.